1. Field of the Invention
The present invention relates to ultrawide-band linear-circular polarization converters, and more particularly relates to an ultrawide-band linear-circular polarization converter which has a noncircular waveguide including a dielectric structure and which is set so that frequency-versus-phase characteristics of the noncircular waveguide and those of the dielectric structure complement each other in a range of the ultrawide-band.
2. Description of the Related Art
Hitherto, in a transmitter-receiver which transmits or receives a satellite broadcasting having a dual-band or an ultrawide-band circularly polarized signal, an ultrawide-band or wide-band linear-circular polarization converter has been used to convert a circularly polarized signal into a linearly polarized signal, and vice versa.
In this case, the dual-band has two frequency bands among satellite broadcasting frequency band at several giga-hertz, such as a frequency band of 12.2 GHz to 12.7 GHz and a frequency band of 19.7 GHz to 20.2 GHz. The wide-band is a frequency band of, for example, 10.7 GHz to 12.75 GHz among the satellite broadcasting frequency band of the above several giga-hertz.
FIGS. 5A and 5B are cross-sectional views showing a first construction example of a known linear-circular polarization converter, in which FIG. 5A is a cross-sectional view perpendicular to the longitudinal direction and FIG. 5B is a cross-sectional view in the longitudinal direction.
As shown in FIGS. 5A and 5B, in the first construction example of a known linear-circular polarization converter, a circular waveguide 51 has a planar dielectric structure 52 provided so as to be along the direction of one diameter thereof. In this case, the planar dielectric structure 52 is provided so as to be along the direction of one diameter of the circular waveguide 51 which is sloped at approximately 45 degrees to the direction of the internal electric field E of the circular waveguide 51. Both side faces extending in the longitudinal direction of the dielectric structure 52 are cut inwardly in a generally triangular shape.
FIGS. 6A and 6B are cross-sectional views showing a second construction example of a known linear-circular polarization converter, in which FIG. 6A is a cross-sectional view perpendicular to the longitudinal direction and FIG. 6B is a cross-sectional view in the longitudinal direction.
As shown in FIGS. 6A and 6B, in the second construction example of a known linear-circular polarization converter, a ridged conductor structure 62 is provided at a part of the inner wall of a circular waveguide 61. In this case, the ridged conductor structure 62 is provided at a position of the inner wall of the circular waveguide 61 which is sloped at approximately 45 degrees to the direction of the internal electric field E of the circular waveguide 61. In the ridged conductor structure 62, the height of an edge part in the longitudinal direction is lower than that of a central part.
In these linear-circular polarization converters, when a linearly polarized signal is input to an input terminal thereof, a circularly polarized signal can be output from an output terminal thereof, and vice versa.
Generally, linear-circular polarization converters can perform a predetermined linear-circular polarization conversion on a polarized signal propagating through the waveguide in a frequency band which causes the phase difference |xcfx86| (=|xcfx86Vxe2x88x92xcfx86H|) between the vertical-polarization phase xcfx86V of the polarized signal and the horizontal-polarization phase xcfx86H thereof to be maintained within a range of 90xc2x0xc2x110xc2x0.
Since the frequency bands of known linear-circular polarization converters causing the phase difference |xcfx86| to be maintained within the range of 90xc2x0xc2x110xc2x0 are relatively narrow frequency ranges, known linear-circular polarization converters cannot be used as wide-band linear-circular polarization converters or ultrawide-band linear-circular polarization converters which activate in a broader frequency range than that of the wide-band linear-circular polarization converters.
Since known linear-circular polarization converters only have a relative frequency band of several percent, favorable conversion characteristics cannot be obtained throughout a relative frequency band of the order of ten percent or a relative frequency band of several tens of percent.
Accordingly, the present invention is made considering such a technical background. It is an object of the present invention to provide an ultrawide-band linear-circular polarization converter for capable of offering favorable frequency-versus-phase characteristics as a linear-circular polarization converter in a frequency range of an ultrawide-band.
To this end, according to a first aspect of the present invention, there is provided an ultrawide-band linear-circular polarization converter in which, in a noncircular waveguide which has negative-phase characteristics in which a phase gradually decreases in accordance with an increase in a frequency over an ultrawide-band frequency range, a dielectric structure which has positive-phase characteristics, in which a phase gradually increases in accordance with an increase in a frequency, having a complementary relationship with the negative-phase characteristics in the ultrawide-band frequency range is provided.
In the ultrawide-band linear-circular polarization converter, the noncircular waveguide may be an elliptic waveguide.
In the ultrawide-band linear-circular polarization converter, the dielectric structure may be provided in the direction of the minor axis of the elliptic waveguide, and the dielectric structure may have edge parts which are thin in the thickness direction and a central part which is thick in the thickness direction.
As described above, according to the present invention, by combining the noncircular waveguide having negative-phase characteristics and the dielectric structure having positive-phase characteristics which complement the negative-phase characteristics, the following advantages are obtained: the ultrawide-band linear-circular polarization converter can be caused to have generally flat frequency-versus-phase characteristics which enable favorable linear-circular polarization conversion to be performed in the ultrawide-band frequency range; and the ultrawide-band linear-circular polarization converter can be obtained, having a simple construction, without causing an increase in manufacturing cost or the like.